With the current growing interest in genome sequencing and mapping, and in PCR applications such as gene probe assays, there is an accelerating demand for oligonucleotide primers. A wide variety of instruments have been developed to meet this demand. A thorough discussion of prior art improvements to the development of methods and apparatus for the chemical synthesis of biopolymers, including polypeptides and oligonucleotides, has been recently provided by Beattie in U.S. Pat. No. 5,175,209 (1992).
In U.S. Pat. No. 5,368,823 (1994), McGraw provides embodiments of an apparatus and method for the automated synthesis of DNA segments utilizing multiple reaction columns, all of which are open at the inlet end to the atmosphere of a reaction chamber. However, the apparatus uses only a single reagent outlet to add reagent to an array of specialized reaction columns. The system is not capable of adding reagent simultaneously to each column, and utilizes costly reaction columns within a complex apparatus.
As another example, Schreuer et aL., (Poster 56, Fifth Intemational Symposium on Solid Phase Synthesis and Combinatorial Chemical Libraries, London, England, U.K. Sep. 2-6 1997) describe an array of pipette tips, each retaining a solid support for oligonucleotide synthesis. The tips are held within a reactor module comprising a holder plate that forms the cover of a waste collecting chamber so that the outlet end of each tip is connected to the waste collecting chamber. Liquids applied from above are held within each tip by surface tension and are removed by a vacuum pulse. The module also employs a specialized perforated plate covering the tips to facilitate flow of an inert atmosphere over the open top ends of the tips. In addition, the tips must be manually mounted and removed from the holder plate. Thus the system utilizes a specialized module and is not easily automated.
Sindelar et al., (Nucleic Acids Res. 23:982 (1995)) describe a system for high-throughput parallel DNA synthesis. However, their apparatus requires a non-standard multichannel reaction chamber module held within a specialized apparatus using a process which is not readily automated.
In U.S. Pat. No. 5,472,672 (1995) Brennan discloses a polymer synthesis apparatus comprising a manifold comprising a complex array of nozzles, micro-shutoff valves, and dispensing tubes, with each nozzle coupled to a reservoir of liquid reagent, and a base assembly having an array of reaction wells. The reliability of the device is compromised by numerous variables which affect the delivery of liquid reagents from nozzles. The apparatus employs a specially fabricated microtiter plate having reaction wells each for retaining a solid support. The outlet end of each well communicates with a catch basin which is coupled to a vacuum pump to purge the reaction wells. The device utilizes a coated sliding gasket, between the reaction wells and nozzles, which is susceptible to wear or rupture. In addition, the apparatus requires carefully controlled pressure regulation between the top ends of the reaction chambers and their outlet ends. The apparatus requires a laborious and possibly imprecise slurry method for depositing solid support matrix into each reaction well; the support is susceptible to being dislodged during use of the apparatus. Thus, the apparatus requires use of nonstandard microtiter plates, and employs a complex manifold and valve system in an apparatus which incorporates a number of potentially unreliable components.